Re: [PATCH v5 14/14] spapr: nested: Introduce cap-nested-papr for Nested PAPR API

[Harsh Prateek Bora]

Hi Nick,

Updated incremental fix below:

On 3/12/24 18:21, Harsh Prateek Bora wrote:
> On 3/12/24 18:17, Harsh Prateek Bora wrote:
> > Hi Nick,
> >
> > On 3/12/24 17:41, Harsh Prateek Bora wrote:
> > > Hi Nick,
> > >
> > > On 3/12/24 17:21, Nicholas Piggin wrote:
> > > > On Fri Mar 8, 2024 at 9:19 PM AEST, Harsh Prateek Bora wrote:
> > > > > Introduce a SPAPR capability cap-nested-papr which enables nested PAPR
> > > > > API for nested guests. This new API is to enable support for KVM on 
> > > > > PowerVM
> > > > > and the support in Linux kernel has already merged upstream.
> > > > >
> > > > > Signed-off-by: Michael Neuling <mikey@neuling.org>
> > > > > Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
> > > > > ---
> > > > >   include/hw/ppc/spapr.h |  6 +++-
> > > > >   hw/ppc/spapr.c         |  2 ++
> > > > >   hw/ppc/spapr_caps.c    | 62 
> > > > > ++++++++++++++++++++++++++++++++++++++++++
> > > > >   hw/ppc/spapr_nested.c  |  8 ++++--
> > > > >   4 files changed, 74 insertions(+), 4 deletions(-)

<snip>

> > > > > +static void cap_nested_papr_apply(SpaprMachineState *spapr,
> > > > > +                                    uint8_t val, Error **errp)
> > > > > +{
> > > > > +    ERRP_GUARD();
> > > > > +    PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
> > > > > +    CPUPPCState *env = &cpu->env;
> > > > > +
> > > > > +    if (!val) {
> > > > > +        /* capability disabled by default */
> > > > > +        return;
> > > > > +    }
> > > > > +
> > > > > +    if (tcg_enabled()) {
> > > > > +        if (!(env->insns_flags2 & PPC2_ISA300)) {
> > > > > +            error_setg(errp, "Nested-PAPR only supported on POWER9 
> > > > > and later");
> > > > > +            error_append_hint(errp,
> > > > > +                              "Try appending -machine 
> > > > > cap-nested-papr=off\n");
> > > > > +            return;
> > > > > +        }
> > > > > +        if (spapr_nested_api(spapr) &&
> > > > > +            spapr_nested_api(spapr) != NESTED_API_PAPR) {
> > > > > +            error_setg(errp, "Nested-HV APIs are mutually 
> > > > > exclusive/incompatible");
> > > > > +            error_append_hint(errp, "Please use either 
> > > > > cap-nested-hv or "
> > > > > +                                    "cap-nested-papr to proceed.\n");
> > > > > +            return;
> > > > > +        } else {
> > > > > +            spapr->nested.api = NESTED_API_PAPR;
> > > > > +        }
> > > > > +
> > > > > +    } else if (kvm_enabled()) {
> > > > > +        /*
> > > > > +         * this gets executed in L1 qemu when L2 is launched,
> > > > > +         * needs kvm-hv support in L1 kernel.
> > > > > +         */
> > > > > +        if (!kvmppc_has_cap_nested_kvm_hv()) {
> > > > > +            error_setg(errp,
> > > > > +                       "KVM implementation does not support 
> > > > > Nested-HV");
> > > > > +        } else if (kvmppc_set_cap_nested_kvm_hv(val) < 0) {
> > > > > +            error_setg(errp, "Error enabling Nested-HV with KVM");
> > > > > +        }
> > > >
> > > > I'll just disable this on KVM for now. With that changed,
> > > >
> > > > Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
> > >
> > > AFAIK, v2 api also expects this capability to be enabled on L1 kernel.
> > > I guess the reason is the L1 implementation has used the same capab and
> > > extended to be used with v2 api. So, this check is needed in L1 Qemu for
> > > now. We may revisit L1 implementation later to see if a change is
> > > appropriate.
> >
> > Please ignore above response. I think my observation was based on 
> > older version of L1 implementation. This doesnt seem to be an issue 
> > with upstream L1. You may disable the kvm_enabled() path for now. I 
> > just tested and it works fine.
>
> Here's the incremental fix:

Updated to keep error_setg for kvm_enabled() case:

diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index d6d5a6b8df..92d8966d60 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -527,18 +527,9 @@ static void cap_nested_papr_apply(SpaprMachineState 
*spapr,
         } else {
             spapr->nested.api = NESTED_API_PAPR;
         }
-
     } else if (kvm_enabled()) {
-        /*
-         * this gets executed in L1 qemu when L2 is launched,
-         * needs kvm-hv support in L1 kernel.
-         */
-        if (!kvmppc_has_cap_nested_kvm_hv()) {
             error_setg(errp,
-                       "KVM implementation does not support Nested-HV");
-        } else if (kvmppc_set_cap_nested_kvm_hv(val) < 0) {
-            error_setg(errp, "Error enabling Nested-HV with KVM");
-        }
+                       "KVM implementation does not support Nested-PAPR");
     }
 }



> regards,
> Harsh
> > regards,
> > Harsh
> >
> > > regards,
> > > Harsh
> > >
> > > > >       }
> > > > >   }
> > > > > @@ -735,6 +787,15 @@ SpaprCapabilityInfo 
> > > > > capability_table[SPAPR_CAP_NUM] = {
> > > > >           .type = "bool",
> > > > >           .apply = cap_nested_kvm_hv_apply,
> > > > >       },
> > > > > +    [SPAPR_CAP_NESTED_PAPR] = {
> > > > > +        .name = "nested-papr",
> > > > > +        .description = "Allow Nested HV (PAPR API)",
> > > > > +        .index = SPAPR_CAP_NESTED_PAPR,
> > > > > +        .get = spapr_cap_get_bool,
> > > > > +        .set = spapr_cap_set_bool,
> > > > > +        .type = "bool",
> > > > > +        .apply = cap_nested_papr_apply,
> > > > > +    },
> > > > >       [SPAPR_CAP_LARGE_DECREMENTER] = {
> > > > >           .name = "large-decr",
> > > > >           .description = "Allow Large Decrementer",
> > > > > @@ -919,6 +980,7 @@ SPAPR_CAP_MIG_STATE(sbbc, SPAPR_CAP_SBBC);
> > > > >   SPAPR_CAP_MIG_STATE(ibs, SPAPR_CAP_IBS);
> > > > >   SPAPR_CAP_MIG_STATE(hpt_maxpagesize, SPAPR_CAP_HPT_MAXPAGESIZE);
> > > > >   SPAPR_CAP_MIG_STATE(nested_kvm_hv, SPAPR_CAP_NESTED_KVM_HV);
> > > > > +SPAPR_CAP_MIG_STATE(nested_papr, SPAPR_CAP_NESTED_PAPR);
> > > > >   SPAPR_CAP_MIG_STATE(large_decr, SPAPR_CAP_LARGE_DECREMENTER);
> > > > >   SPAPR_CAP_MIG_STATE(ccf_assist, SPAPR_CAP_CCF_ASSIST);
> > > > >   SPAPR_CAP_MIG_STATE(fwnmi, SPAPR_CAP_FWNMI);
> > > > > diff --git a/hw/ppc/spapr_nested.c b/hw/ppc/spapr_nested.c
> > > > > index 597dba7fdc..8db9dc19e3 100644
> > > > > --- a/hw/ppc/spapr_nested.c
> > > > > +++ b/hw/ppc/spapr_nested.c
> > > > > @@ -13,13 +13,15 @@
> > > > >   void spapr_nested_reset(SpaprMachineState *spapr)
> > > > >   {
> > > > >       if (spapr_get_cap(spapr, SPAPR_CAP_NESTED_KVM_HV)) {
> > > > > -        spapr->nested.api = NESTED_API_KVM_HV;
> > > > >           spapr_unregister_nested_hv();
> > > > >           spapr_register_nested_hv();
> > > > > -    } else {
> > > > > -        spapr->nested.api = 0;
> > > > > +    } else if (spapr_get_cap(spapr, SPAPR_CAP_NESTED_PAPR)) {
> > > > >           spapr->nested.capabilities_set = false;
> > > > > +        spapr_unregister_nested_papr();
> > > > > +        spapr_register_nested_papr();
> > > > >           spapr_nested_gsb_init();
> > > > > +    } else {
> > > > > +        spapr->nested.api = 0;
> > > > >       }
> > > > >   }